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The precision measurement of the primordial helium abundance $Y_p$ is apowerful probe of the early Universe. The most common way to determine $Y_p$ isanalyses of observations of metal-poor \HII regions found in blue compact dwarfgalaxies. We present the spectroscopic sample of 100 \HII regions collectedfrom the Sloan Digital Sky Survey. The final analysed sample consists of oursample and HeBCD database from Izotov et al. 2007. We use a self-consistentprocedure to determine physical conditions, current helium abundances, andmetallicities of the \HII regions. From a regression to zero metallicity, wehave obtained $Y_p = 0.2462 \pm 0.0022$ which is one of the most stringentconstraints obtained with such methods up to date and is in a good agreementwith the Planck result $Y_{\rm p}^{\it {Planck}} = 0.2471 \pm 0.0003$. Usingthe determined value of $Y_p$ and the primordial deuterium abundance taken fromParticle Data Group (Zyla et al. 2020) we put a constraint on the effectivenumber of neutrino species $N_{\rm eff} = 2.95 \pm 0.16$ which is consistentwith the Planck one $N_{\rm eff} = 2.99 \pm 0.17$. Further increase ofstatistics potentially allows us to achieve Planck accuracy, which in turn willbecome a powerful tool for studying the self-consistency of the StandardCosmological Model and/or physics beyond.

A new determination of the primordial helium abundance using the analyses of HII region spectra from SDSS